Skin care formulations containing copolymers, inorganic metal oxide particles, and silicones

ABSTRACT

Provided are skin care compositions that are useful as SPF and UV absorption boosters in formulations containing inorganic metal oxides. The compositions comprise (a) 0.1 to 20 weight % inorganic metal oxide particles, based on the weight of the composition, (b) 0.1 to 15 weight % copolymer particles dispersed in an aqueous medium, wherein the copolymer particles comprise polymerized units derived from (i) 0.1 to 20 weight % of phosphorus acid monomers, and (ii) 80 to 99.9 weight % of comonomers, (c) 0.1 to 35 weight % silicone fluid, based on the total weight of the composition, and (d) a dermatologically acceptable carrier. Also provided are methods of protecting skin from UVA and UVB damage comprising topically administering such compositions to the skin, and methods of boosting the SPF or UV absorption of a sunscreen composition containing inorganic metal oxide particles comprising including such copolymer particles in the composition.

FIELD OF THE INVENTION

This invention relates generally to copolymers that are useful in skincare formulations. The skin care formulations contain copolymerparticles bearing phosphorus acid groups with inorganic metal oxideparticles and silicones.

BACKGROUND

Skin care compositions contain a variety of additives that provide awide array of benefits to the composition. Sunscreen compositions inparticular contain additives that offer protection from ultraviolet(“UV”) radiation, which can damage the skin. UV radiation can beclassified as UVA (long wave; i.e., wavelengths of 320-400 nm) and UVB(short wave; i.e., wavelengths of 290 to 320 nm). The efficacy ofsunscreen formulations is measured by its sun protection factor (“SPF”).Since both UVA and UVB forms of radiation are harmful, sunscreenformulations offer protection from both kinds of rays. Inorganic metaloxide particles, such as titanium dioxide and zinc oxide, provideabsorption of UVA and UVB radiation and to this end are commonlyincorporated into sunscreen formulations. Inorganic metal oxides,however, can cause negative aesthetic qualities such as poor sensorialfeel and an undesirable white appearance, both of which may be due toagglomeration of particles and poor distribution on skin. Silicones havebeen utilized to improve the sensorial feel of skin care compositionsand exhibit excellent spreading of the formulation. Nonetheless,silicones and inorganic metal oxides have limited compatibility at highlevels with in skin care compositions.

Durability of sunscreen formulations is another consideration that hasbeen addressed in the art. For example, U.S. Pat. No. 6,384,104discloses UV radiation absorbing compositions containing a latex for thepurpose of maintaining storage stability of sunscreen formulations whenadded to personal care compositions. The prior art does not, however,disclose a formulation containing silicones, inorganic metal oxideparticles, and copolymer particles according to the present inventionwhich gives superior results as a UV absorption booster.

Accordingly, there is a need to develop new sunscreen compositionsincluding sunscreen boosters which will help provide a high SPF, whileimproving aesthetic qualities of such formulations such as sensorialfeel and visual appearance.

STATEMENT OF INVENTION

One aspect of the invention provides a skin care composition comprising(a) 0.1 to 20 weight % inorganic metal oxide particles, based on theweight of the composition, (b) 0.1 to 15 weight % copolymer particlesdispersed in an aqueous medium, based on the weight of the composition,wherein the copolymer particles comprise polymerized units derived from(i) 0.1 to 20 weight % of phosphorus acid monomers, and (ii) 80 to 99.9weight % of comonomers, (c) 0.1 to 35 weight % silicone fluid, based onthe total weight of the composition, and (d) a dermatologicallyacceptable carrier.

In another aspect, the invention provides a method for protecting skinfrom UVA and UVB damage comprising topically administering to the skin asunscreen composition comprising (a) 0.1 to 20 weight % inorganic metaloxide particles, based on the weight of the composition, (b) 0.1 to 15weight % copolymer particles dispersed in an aqueous medium, based onthe weight of the composition, wherein the copolymer particles comprisepolymerized units derived from (i) 0.1 to 20 weight % of phosphorus acidmonomers, and (ii) 80 to 99.9 weight % of comonomers, (c) 0.1 to 35weight % silicone fluid, based on the total weight of the composition,and (d) a dermatologically acceptable carrier.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows scanning electron micrographs acquired in theback-scattered mode of titanium dioxide high silicone formulations: (C1)comparative formulation without copolymer particles; (C2) comparativeformulation containing comparative copolymer particles; and (C3)exemplary formulation containing copolymer particles in accordance withthe present invention.

FIG. 2 shows asymmetric flow field fractionation (A4F) LS90 fractogramsof titanium dioxide high silicone formulations: (C1) comparativeformulation without copolymer particles; (C2) comparative formulationcontaining comparative copolymer particles; and (C3) exemplaryformulation containing copolymer particles in accordance with thepresent invention.

FIG. 3 shows asymmetric flow field fractionation (A4F) LS90 fractogramsof titanium dioxide high silicone formulations: (C1) comparativeformulation without copolymer particles; and (C3) exemplary formulationcontaining copolymer particles in accordance with the present invention.

FIG. 4 shows asymmetric flow field fractionation (A4F) LS90 fractogramsof titanium dioxide high silicone formulations: (C3) comparativeformulation without copolymer particles; and (E2) exemplary formulationcontaining copolymer particles in accordance with the present invention.

DETAILED DESCRIPTION

The inventors have now surprisingly found copolymer particles comprisingpolymerized units derived from phosphorus acid monomers provide a boostin SPF or UV absorption in sunscreen formulations containing inorganicmetal oxides, while also improving the aesthetic qualities, e.g.,sensorial feel and visual appearance, of formulations includingsilicones when applied to the skin. Accordingly, the present inventionprovides in one aspect a skin care composition comprising inorganicmetal oxide particles, copolymer particles dispersed in an aqueousmedium comprising polymerized units of phosphorus acid monomers andcomonomers, silicones, and a dermatologically acceptable carrier.

While not wishing to be bound by theory, it is believed that thecopolymer particles enhance the compatibility between the inorganicmetal oxide particles and silicones that are included in the formulationby forming a well-dispersed matrix upon drying at the interstices of thesilicone domains. The phosphate functionality in the copolymer particlesimproves the dispersion of the inorganic metal oxide particles into thepolymer matrix through interactions between the surface of the TiO₂ andthe copolymer particles. More specifically, it is believed that onlycertain portions of the copolymer particles are adsorbed, with theircorresponding loops and tails extending out into the solution. As theparticles approach each other, their adsorbed layers become crowded;this provide an effective steric barrier that prevents flocculation. Asa result, energy is increased giving rise to repulsive forces that helpto keep the particles separated from each other, thereby allowing for astable and uniform silicone sunscreen with inorganic metal oxideparticles to be formulated in the presence of the inventive copolymerparticles.

In the present invention, “skin care compositions” is intended to referto compositions for leave on application to the skin, such as lotions,creams, gels, gel creams, serums, toners, wipes, liquid foundations,make-ups, tinted moisturizer, oils, face/body sprays, topical medicines,and sunscreen compositions. “Sunscreen compositions” refers tocompositions that protect the skin from UV damage. Preferably, the skincare composition is cosmetically acceptable. “Cosmetically acceptable”refers to ingredients typically used in personal care compositions, andis intended to underscore that materials that are toxic when present inthe amounts typically found in personal care compositions are notcontemplated as part of the present invention. The compositions of theinvention may be manufactured by processes well known in the art, forexample, by means of conventional mixing, dissolving, granulating,emulsifying, encapsulating, entrapping or lyophilizing processes.

As used herein, the term “polymer” refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differenttype. The generic term “polymer” includes the terms “homopolymer,”“copolymer,” and “terpolymer.” As used herein, the term “polymerizedunits derived from” refers to polymer molecules that are synthesizedaccording to polymerization techniques wherein a product polymercontains “polymerized units derived from” the constituent monomers whichare the starting materials for the polymerization reactions.

As used herein, the term “(meth)acrylate” refers to either acrylate ormethacrylate, and the term “(meth)acrylic” refers to either acrylic ormethacrylic.

As used herein, the term “phosphorus acid group” refers to a phosphorusoxo acid having a POH moiety in which the hydrogen atom is ionizable.Also included in the term “phosphorus acid group” are salts of thephosphorus oxo acid. In its salt or basic form, the phosphorus acidgroup has a cation such as a metal ion or an ammonium ion replacing atleast one acid proton. Examples of phosphorus acid groups include groupsformed from phosphinic acid, phosphonic acid, phosphoric acid,pyrophosphonic acid, pyrophosphoric acid, partial esters thereof, andsalts thereof.

As used herein, the terms “glass transition temperature” or “T_(g)”refers to the temperature at or above which a glassy polymer willundergo segmental motion of the polymer chain. Glass transitiontemperatures of a polymer can be estimated by the Fox equation (Bulletinof the American Physical Society, 1 (3) Page 123 (1956)) as follows:1/T _(g) =w ₁ /T _(g(1)) +w ₂ /T _(g(2))

For a copolymer, w₁ and w₂ refer to the weight fraction of the twocomonomers, and T_(g(1)) and T_(g(2)) refer to the glass transitiontemperatures of the two corresponding homopolymers made from themonomers. For polymers containing three or more monomers, additionalterms are added (w_(n)/T_(g(n))). The T_((g)) of a polymer can also becalculated by using appropriate values for the glass transitiontemperatures of homopolymers, which may be found, for example, in“Polymer Handbook,” edited by J. Brandrup and E. H. Immergut,Interscience Publishers. The T_(g) of a polymer can also be measured byvarious techniques, including, for example, differential scanningcalorimetry (“DSC”). The values of T_(g) reported herein are measured byDSC.

The inventive skin care compositions contain inorganic metal oxideparticles. Suitable inorganic metal oxides include, for example, zincoxide (ZnO), titanium dioxide (TiO₂), and mixtures thereof. In certainembodiments, the inorganic metal oxide particles are pigment grade ZnOor pigment grade TiO₂. In certain embodiments, the inorganic metal oxideparticles are transparent ZnO or transparent TiO₂. Most inorganic metaloxides used in sunscreen formulations produce a cosmetically undesirablewhite appearance caused by light scattering. Thus, as used herein, theterm “transparent” inorganic metal oxide sunscreen particle refers toinorganic metal oxide particles produced by a variety of processingconditions which render compositions containing such particles as clear,or more transparent than pigment grade, upon application. Suitable ZnOparticles include, for example, those commercially available under thetrade names Z-COTE from BASF Corporation, ZINCLEAR IM from AntariaLimited, and Z-CLEAR from Actifirm. Suitable TiO₂ particles include, forexample, those commercially available under the trade names TIPAQUE andTTO-51(A) from Ishiharra Sangyo Kaisha, Ltd., T-COTE from BASFCorporation, UFTR (from Miyoshi Kasei), and SOLAVEIL CLARUS fromUniquema. In certain embodiments, the skin care compositions includeinorganic metal oxide particles in an amount of from 0.1 to 20 weight %,preferably from 0.5 to 18 weight %, and more preferably from 1 to 15weight %, by weight of the composition.

The skin care compositions of the present invention also containcopolymer particles bearing phosphorus acid groups pendant to thepolymer backbone. These phosphorus acid groups are referred to herein as“first phosphorus acid groups.” The copolymer particles are dispersed inan aqueous medium, and are insoluble in the aqueous medium. Thecopolymer particles are addition polymers, which comprise polymerizedunits derived from (i) ethylenically unsaturated monomers having aphosphorus acid groups, referred to herein as “phosphorus acidmonomers,” and (ii) ethylenically unsaturated monomers, referred toherein as “comonomers.”

The phosphorus acid monomers contain at least one ethylenic unsaturationand a phosphorus acid group. The phosphorus acid monomer may be in theacid form or as a salt of the phosphorus acid group. Suitable phosphorusacid monomers include, for example:

wherein R is an organic group containing an acryloxy, methacryloxy, or avinyl group; and R′ and R″ are independently selected from H and asecond organic group. The second organic group maybe saturated orunsaturated. Suitable phosphorus acid monomers include, for example,dihydrogen phosphate-functional monomers, e.g., dihydrogen phosphateesters of an alcohol in which the alcohol also contains a polymerizablevinyl or olefinic group (e.g., allyl phosphate, mono- or diphosphate ofbis(hydroxyl-methyl)fumarate or itaconate), and derivatives of(meth)acrylic acid esters, e.g., phosphates of hydroxyalkyl(meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl(meth)acrylates). Other suitable phosphorus acid monomers include, forexample phosphonate functional monomers, e.g., vinyl phosphonic acid,allyl phosphonic acid, α-phosphonostyrene, and2-methylacrylamido-2-methylpropanephosphonic acid. Further suitablephosphorus functional monomers include, for example, 1,2-ethylenicallyunsaturated (hydroxy)phosphinylalkyl (meth)acrylate monomers, e.g.,(hydroxy)phosphinylmethyl methacrylate. In certain preferredembodiments, the phosphorus acid monomers comprise dihydrogen phosphatemonomers, e.g., 2-phosphoethyl (meth)acrylate, 2-phosphopropyl(meth)acrylate, 3-phosphopropyl (meth)acrylate, and3-phospho-2-hydroxypropyl (meth)acrylate. In certain embodiments, theinventive copolymers comprise polymerized units of phosphorus acidmonomers in an amount of at least 0.1 weight %, preferably at least 0.5weight %, and more preferably at least 1 weight %, by weight of thecopolymer. In certain embodiments, the inventive copolymer comprisepolymerized units of phosphorus acid monomers in an amount of no morethan 20 weight %, preferably no more than 10 weight %, and morepreferably no more than 6 weight %.

The comonomers are ethylenically unsaturated monomers which are notphosphorus acid monomers and are copolymerizable with an ethylenicallyunsaturated phosphorus acid monomer. Suitable comonomers include, forexample, styrene, butadiene, α-methyl styrene, vinyl toluene, vinylnaphthalene, ethylene, propylene, vinyl acetate, vinyl versatate, vinylchloride, vinylidene chloride, acrylonitrile, methacrylonitrile,(meth)acrylamide, various C₁-C₄₀ alkyl esters of (meth)acrylic acid(e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate,n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl(meth)acrylate, tetradecyl (meth)acrylate, lauryl (meth)acrylate, oleyl(meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate)),and other (meth)acrylates (e.g., isobornyl (meth)acrylate, benzyl(meth)acrylate, phenyl (meth)acrylate, 2-bromoethyl (meth)acrylate,2-phenylethyl (meth)acrylate, and 1-naphthyl (meth)acrylate)),alkoxyalkyl (meth)acrylates, e.g., ethoxyethyl (meth)acrylate, mono-,di-, trialkyl esters of ethylenically unsaturated di- and tricarboxylicacids and anhydrides (e.g., ethyl maleate, dimethyl fumarate, trimethylaconitate, and ethyl methyl itaconate), and carboxylic acid containingmonomers, e.g., (meth)acrylic acid, itaconic acid, fumaric acid, andmaleic acid. In certain embodiments, the inventive copolymers comprisepolymerized units of comonomers in an amount of at least 80 weight %,preferably at least 90 weight %, and more preferably at least 94 weight%, by weight of the copolymer. In certain embodiments, the inventivecopolymer comprise polymerized units of comonomers in an amount of nomore than 99.9 weight %, preferably no more than 99.5 weight %, and morepreferably no more than 99 weight %.

In certain embodiments, the polymer may be a crosslinked polymer,wherein a crosslinker, such as a monomer having two or morenon-conjugated ethylenically unsaturated groups, is included with thecopolymer components during polymerization. Suitable crosslinkermonomers include, for example, di- or tri-allyl ethers and di- ortri-(meth)acrylyl esters of diols or polyols (e.g., trimethylolpropanediallyl ether, ethylene glycol dimethacrylate), di- or tri-allyl estersof di- or tri-acids, allyl (meth)acrylate, divinyl sulfone, triallylphosphate, divinylaromatics (e.g., divinylbenzene). In certainembodiments, the inventive copolymers comprise polymerized units ofcrosslinker monomers in an amount of no more than 5 weight %, preferablyno more than 3 weight %, more preferably no more than 2 weight %, andeven more preferably no more than 1 weight %, by weight of thecopolymer.

Polymer molecular weights can be measured by standard methods such as,for example, size exclusion chromatography or intrinsic viscosity. Incertain embodiments, the copolymer particles of the present inventionhave a weight average molecular weight (M_(w)) of 5,000,000 or less,preferably 3,000,000 or less, more preferably 2,000,000 or less, andeven more preferably 1,000,000 or less, as measured by gel permeationchromatography. In certain embodiments, the copolymer particles have aM_(w) of 5,000 or more, preferably 50,000 or more, and more preferably100,000 or more, as measured by gel permeation chromatography. Copolymerparticles suitable for use in the inventive skin care compositions haveT_(g) values in the range of from 25° C. to 150° C., preferably from 50°C. to 150° C., and more preferably from 60° C. to 100° C. In certainembodiments, the inventive copolymer particles have an average diameterin a range of from 10 nm to 20 microns, preferably from 20 nm to 1micron, and more preferably from 50 nm to 500 nm. The diameters of thecopolymer particles may be characterized by distributions such asunimodal or multimodal, including bimodal. The average diameter of thecopolymer particles may be determined by a light scattering technique.

In certain embodiments, the inventive skin care composition includescopolymer particles in an amount of from 0.1 to 15 weight %, preferablyfrom 0.5 to 10 weight %, and more preferably from 1 to 8 weight, byweight of the composition. In certain embodiments, the skin carecomposition includes the inorganic metal oxide and copolymer particlesin a weight ratio of from 2:8 to 8:2, preferably from 3:7 to 7:3, andmore preferably from 4:6 to 6:4.

Suitable polymerization techniques for preparing the copolymer particlescontained in the inventive skin care compositions include, for example,emulsion polymerization and solution polymerization, preferably emulsionpolymerization, as disclosed in U.S. Pat. No. 6,710,161. Aqueousemulsion polymerization processes typically are conducted in an aqueousreaction mixture, which contains at least one monomer and varioussynthesis adjuvants, such as the free radical sources, buffers, andreductants in an aqueous reaction medium. In certain embodiments, achain transfer agent may be used to limit molecular weight. The aqueousreaction medium is the continuous fluid phase of the aqueous reactionmixture and contains more than 50 weight % water and optionally one ormore water miscible solvents, based on the weight of the aqueousreaction medium. Suitable water miscible solvents include, for example,methanol, ethanol, propanol, acetone, ethylene glycol ethyl ethers,propylene glycol propyl ethers, and diacetone alcohol. In certainembodiments, the aqueous reaction medium contains more than 90 weight %water, preferably more than 95 weight % water, and more preferably morethan 98 weight % water, based on the weight of the aqueous reactionmedium. In certain embodiments, the aqueous reaction medium has a pH ofless than or equal to 8, and preferably having a pH of less than orequal to 4.

The polymerization process may be conducted as a batch, semicontinuous,or continuous process. In certain embodiments, the polymer is formed ina two stage reaction. In certain embodiments, the first stage comprisespolymerizing 1 to 10 weight % of phosphorus acid monomers, 99 to 80weight % comonomers, and 0 to 5 weight % of crosslinker, based on thetotal weight of monomers polymerized in the first stage. In certainembodiments, the second stage comprises polymerizing 95 to 100 weight %comonomers, and 0 to 5 weight % of crosslinker, based on the totalweight of monomers polymerized in the second stage. In certainembodiments, the phosphorus acid monomers comprise a phosphoethylmethacrylate. In certain embodiments, the comonomers comprise at leastone of butyl acrylate, methyl methacrylate, and methacrylic acid. Incertain embodiments, the crosslinker comprises allyl methacrylate. Incertain embodiments, the total ratio of monomers polymerized in stage 1and stage 2 ranges from 20:80 to 80:20, preferably from 25:75 to 75:25,and more preferably from 30:70 to 70:30.

The skin care compositions of the present invention also containsilicone fluid. Suitable silicone fluids include, for example, lowviscosity silicones and siloxanes, e.g., volatile methyl siloxanes,volatile ethyl siloxanes, and volatile methyl ethyl siloxanes having aviscosity at 25° C. in the range of 1 to 1,000 mm²/sec. In certainembodiments, the silicone fluids comprise at least one ofhexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,octamethyltrisiloxane, decamethyltetrasiloxane,dodecamethylpentasiloxane, tetradecamethylhexasiloxane,hexadeamethylheptasiloxane,heptamethyl-3-{(trimethylsily)oxy)}trisiloxane,hexamethyl-3,3,bis{(trimethylsilyl)oxy}trisiloxanepentamethyl{(trimethylsilyl)oxy}cyclotrisiloxane, polydimethylsiloxanes,polyethylsiloxanes, polymethylethylsiloxanes, polymethylphenylsiloxanes,and polydiphenylsiloxanes. In certain embodiments, the silicone fluidscomprise a functionalized polysiloxane. Suitable functionalizedpolysiloxanes include, for example, amino functional siloxane fluids,carbinol functional siloxane fluids, carboxy functional siloxane fluids,chloroalkyl functional siloxane fluids, epoxy functional siloxanefluids, glycol functional siloxane fluids, ketal functional siloxanefluids, mercapto functional siloxane fluids, methyl ester functionalsiloxane fluids, perfluoro functional siloxane fluids, polyisobutylene(PIB) functional siloxane fluids, silanol functional siloxanes, andvinyl functional siloxane fluids. In certain preferred embodiments, thesilicone fluid comprises at least one of XIAMETER PMX-200, XIAMETERPMX-0225, XIAMETER PMX-0245, XIAMETER PMX-0344, XIAMETER PMX-9027,XIAMETER OFX-8220, DOW CORNING 9045 Silicone Elastomer Blend, and DOWCORNING 9040 Silicone Elastomer Blend, all of which are available fromThe Dow Chemical Company/Dow Corning. In certain embodiments, thesilicone fluid is present in an amount of at least 0.1 weight %, basedon the total weight of the composition. In certain embodiments, thesilicone fluid is present in an amount of no more than 30 weight %, or25 weight %, or 20 weight %, or 15 weight %, or 10 weight %, or 5 weight%, or 3 weight %, based on the total weight of the composition.

The inventive skin care compositions contain the copolymer particlesdispersed in an aqueous medium. The aqueous medium may containcosolvents, e.g., water miscible cosolvents. Suitable water misciblecosolvents include, for example, methanol, ethanol, propanol, acetone,ethylene glycol ethyl ethers, propylene glycol propyl ethers, anddiacetone alcohol; and water immiscible solvents such as propyl acetate,butyl acetate, methyl isoamyl ketone, amyl acetate, diisobutyl ketone,xylene, toluene, butanol, and mineral spirits. The pH of the skin carecomposition may be in the range of 3 to 11.

In certain embodiments, the skin care composition is characterized asbeing substantially-free of water soluble phosphorus acid compounds.Water soluble phosphorus acid compounds contain phosphorus acid groups,referred to herein as “second phosphorus acid groups.” At a pH of 5 andabove, the water soluble phosphorus acid compounds are contained as asolubilized component of the aqueous medium. The water solublephosphorus acid compounds include inorganic phosphorus acid compoundsand organic phosphorus acid compounds. Inorganic phosphorus acidcompounds include phosphorus oxo acids such as phosphoric acid,phosphorus acid, hydrophosphorous acid, orthophosphoric acid,pyrophosphoric acid, and salts thereof. Organic phosphorus acidcompounds contain at least one phosphorus acid group attached to anorganic moiety and include both unsaturated organic phosphorus acidcompounds such as phosphorus acid monomers; and saturated organicphosphorus acid compounds such as partial esters of phosphorus oxo acidssuch as HOCH₂CH₂OP(O)(OH)₂, methyl phosphonic acid, and water solublepolymer bearing phosphorus acid groups. The water soluble polymerbearing phosphorus acid groups are addition polymers containing at leasttwo phosphorus acid groups that are independently located pendant to thebackbone of the water soluble polymer or in a terminal position. Thewater soluble polymer bearing phosphorus acid groups may be ahomopolymer or a copolymer, and has a degree of polymerization of atleast 2. As used herein, “saturated phosphorus acid compounds” arecompounds selected from inorganic phosphorus acid compounds andsaturated organic phosphorus acid compounds. As used herein,“substantially-free of water soluble phosphorus acid compounds” refersto a level of water soluble phosphorus acid compounds in the polymercomposition as defined by the ratio of equivalents of second phosphorusacid groups to equivalents of first phosphorus acid groups in a rangehaving an upper value of 0.8, preferably 0.7, and more preferably 0.5;and may have a lower value in the range of 0.1, preferably 0.05, andmore preferably zero. In one embodiment, the ratio of equivalents ofsecond phosphorus acid groups to equivalents of first phosphorus acidgroups is in the range of less than or equal to 0.8, preferably lessthan or equal to 0.7, and more preferably less than or equal to 0.5. Theratio of equivalents of second phosphorus acid groups to equivalents offirst phosphorus acid groups in the skin care composition is determinedby inductively coupled plasma spectroscopy detection of phosphorusatoms, as disclosed in U.S. Pat. No. 6,710,161. The first phosphorusacid groups and the second phosphorus acid groups may be the same typeof phosphorus acid or may be different; for example, the firstphosphorus acid groups may be formed from phosphoric acid and the secondphosphorus acid groups may be formed from phosphonic acid.

In certain embodiments of the present invention, the inventive skin carecomposition comprises a composite particle composition wherein thecopolymer particles are adsorbed onto the surface of the inorganic metaloxide particles to form composite particles. While not wishing to bebound by theory, it is believed that the contact between adjacentinorganic metal oxide particles is minimized due to the adsorption ofcopolymer particles onto the surface of each inorganic metal oxideparticle. The copolymer particles may fully cover the surface of theinorganic metal oxide particle to provide an encapsulating layer or maypartially cover the inorganic metal oxide particle surface. Thecomposite particles are useful for providing sunscreen agents withimproved absorbance of UV radiation and increased SPF performancecompared to compositions containing equivalent levels of unalteredinorganic metal oxide particles (i.e., not containing compositeparticles).

The composite particles may include copolymer particles with a singlepolymer phase or two-phase copolymer particles that have the phosphorusacid groups in one or more phases in contact with the exterior of thecopolymer particle. In one embodiment, the composite particle containstwo-phase copolymer particles having one polymer phase that does notcompletely encapsulate the second polymer phase.

In certain embodiments, the composite particles contain copolymerparticles having an average particle diameter in the range of 40 nm to50 μm, preferably in the range of 50 nm to 5 μm, and more preferably inthe range of 60 nm to 1 μm. In certain embodiments, the compositeparticles contain copolymer particles having T_(g) values in the rangeof from 25° C. to 150° C., preferably from 50° C. to 150° C., and morepreferably from 60° C. to 100° C. In certain embodiments, the pH of theinventive skin care compositions containing the composite particles maybe in the range of from 3 to 10, and preferably a pH of from 7 to 9.

Inventive skin care compositions including the composite particlescontaining the copolymer particles may be prepared by first admixing afirst aqueous medium containing a dispersion of inorganic metal oxideparticles, and a copolymer composition containing the copolymerparticles. The copolymer particles are allowed sufficient time to adsorbto the inorganic metal oxide particles to form the composite particles.The adsorption of the copolymer particles to the inorganic metal oxideparticles is believed to be spontaneous and will continue until thecopolymer particles are completely adsorbed to the surfaces of theinorganic metal oxide particles, the surfaces of the inorganic metaloxide particles are completely covered with copolymer particles, oruntil an equilibrium is achieved between adsorbed copolymer particlesand copolymer particles remaining dispersed in the aqueous medium of thecomposite particle composition.

Skin care compositions of the invention also include a dermatologicallyacceptable carrier. Such material is typically characterized as acarrier or a diluent that does not cause significant irritation to theskin and does not negate the activity and properties of active agent(s)in the composition. Examples of dermatologically acceptable carriersthat are useful in the invention include, without limitation, water,such as deionized or distilled water, emulsions, such as oil-in-water orwater-in-oil emulsions, alcohols, such as ethanol, isopropanol or thelike, glycols, such as propylene glycol, glycerin or the like, creams,aqueous solutions, oils, ointments, pastes, gels, lotions, milks, foams,suspensions, powders, or mixtures thereof. In some embodiments, thecomposition contains from about 99.99 to about 50 percent by weight ofthe dermatologically acceptable carrier, based on the total weight ofthe composition.

The skin care compositions of the invention may also include sunscreenactives in addition to the inorganic metal oxide particles. Suitableadditional sunscreen actives include, for example, para aminobenzoicacid, avobenzone, cinoxate, dioxybenzone, homosalate, menthylanthranilate, octocrylene, octyl methoxycinnamate, octyl salicylate,oxybenzone, padimate 0, phenylbenzimidazole sulfonic acid,sulisobenzone, trolamine salicylate, titanium dioxide, zinc oxide,benzophenones, benzylidenes, salicylates, or other known UV filters,including diethanolamine methoxycinnamate, digalloy trioleate, ethyldihydroxypropyl PAB A, glyceryl aminobenzoate, and lawsone withdihydroxy acetone and red petrolatum.

The skin care compositions of the invention may also include otheringredients known in the art of sunscreen formulations including, forexample, a thickener, emollients, an emulsifier, a humectant, asurfactant, a suspending agent, a film forming agent, a lowermonoalcoholic polyol, a high boiling point solvent, a propellant, amineral oil, silicon feel modifiers, or mixtures thereof. The amount ofoptional ingredients effective for achieving the desired propertyprovided by such ingredients can be readily determined by one skilled inthe art.

Other additives may be included in the compositions of the inventionsuch as, but not limited to, abrasives, absorbents, aesthetic componentssuch as fragrances, pigments, colorings/colorants, essential oils, skinsensates, astringents (e.g., clove oil, menthol, camphor, eucalyptusoil, eugenol, menthyl lactate, witch hazel distillate), preservatives,anti-caking agents, a foam building agent, antifoaming agents,antimicrobial agents (e.g., iodopropyl butylcarbamate), antioxidants,binders, biological additives, buffering agents, bulking agents,chelating agents, chemical additives, colorants, cosmetic astringents,cosmetic biocides, denaturants, drug astringents, external analgesics,film formers or materials, e.g., polymers, for aiding the film-formingproperties and substantivity of the composition (e.g., copolymer ofeicosene and vinyl pyrrolidone), opacifying agents, pH adjusters,propellants, reducing agents, sequestrants, skin bleaching andlightening agents (e.g., hydroquinone, kojic acid, ascorbic acid,magnesium ascorbyl phosphate, ascorbyl glucosamine), skin-conditioningagents (e.g., humectants, including miscellaneous and occlusive), skinsoothing and/or healing agents (e.g., panthenol and derivatives (e.g.,ethyl panthenol), aloe vera, pantothenic acid and its derivatives,allantoin, bisabolol, and dipotassium glycyrrhizinate), skin treatingagents, and vitamins (e.g., Vitamin C) and derivatives thereof. Theamount of option ingredients effective for achieving the desiredproperty provided by such ingredients can be readily determined by oneskilled in the art.

As noted above, skin care compositions of the present invention arehighly effective as SPF and UV absorption boosters. Accordingly, theskin care compositions of the present invention are useful for thetreatment and protection of skin, including, for example, protectionfrom UV damage, moisturization of the skin, prevention and treatment ofdry skin, protection of sensitive skin, improvement of skin tone andtexture, masking imperfections, and inhibition of trans-epidermal waterloss. Thus, in one aspect the present invention provides that the skincare compositions may be used in a method for protecting skin from UVAand UVB damage comprising topically administering to the skin acomposition comprising (a) 0.1 to 20 weight % inorganic metal oxideparticles, based on the weight of the composition, (b) 0.1 to 15 weight% copolymer particles as described herein dispersed in an aqueousmedium, based on the weight of the composition, (c) 0.1 to 35 weight %silicone particles, based on the total weight of the composition, and(d) a dermatologically acceptable carrier. The compositions may also beused in a method for boosting the SPF or UV absorption of a sunscreencomposition containing inorganic metal oxide particles comprisingincluding in the composition copolymer particles as described herein inan aqueous medium. In certain embodiments, the inventive sunscreencompositions containing inorganic metal oxide particles and copolymersdescribed herein have an SPF that is more than 25% higher, andpreferably more than 50% higher, than compositions containing equivalentlevels of unaltered inorganic metal oxide particles (i.e., notcontaining composite particles)

In practicing the methods of the invention, the skin care compositionsare generally administered topically by applying or spreading thecompositions onto the skin. A person of ordinary skill in the art canreadily determine the frequency with which the compositions should beapplied. The frequency may depend, for example, on the level of exposureto UV light that an individual is likely to encounter in a given dayand/or the sensitivity of the individual to UV light. By way ofnon-limiting example, administration on a frequency of at least once perday may be desirable.

Some embodiments of the invention will now be described in detail in thefollowing Examples.

EXAMPLES Example 1

Preparation of Exemplary and Comparative Copolymer Particles

Comparative copolymer particles and exemplary copolymer particles inaccordance with the present invention contain the components recited inTable 1.

TABLE 1 Comparative and Exemplary Copolymer Particles Sample Monomer (wt%) PE Stage 1 (35%): 11.2 BA/83.5 MMA/5.1 PEM/0.2 MAA Stage 2 (65%):14.1 BA/85.7 MMA/0.2 MAA PC* Stage 1 (35%): 11.8 BA/88 MMA/0.2 MAA Stage2 (65%): 14.1 BA/85.7 MMA/0.2 MAA *Comparative MMA = methyl methacrylateMAA = methacrylic acid BA = butyl acrylate PEM = phosphoethylmethacrylate

For polymer PE, a Stage 1 monomer emulsion was prepared by mixing 65.5 gDI water, 16.5 g (30% active) anionic surfactant-A (surfactant having anaverage composition of lauryl-(ethylene oxide)₄ sodium sulfate; 30 wt %solids), 27.1 g BA, 202.4 g MMA, 0.5 g MAA, and 16.2 g PEM. A Stage 2monomer emulsion was then prepared by mixing 136 g DI water, 15.4 g (30%active) anionic surfactant A, 64.5 g BA, 392.2 g MMA, and 1.0 g MAA. A 3liter reactor, four-necked round bottom flask equipped with a paddlestirrer, a thermocouple, nitrogen inlet, and reflux condenser wasassembled. To the flask was added 1,170 g DI water and 16.5 g (30%active) anionic surfactant A, and stirring was started. The contents ofthe flask were heated to 84° C. under a nitrogen atmosphere. A solutionof 1.4 g NaPS in 13 g DI water was added. The stage 1 monomer emulsionwas fed into the reactor over 40 minutes. A solution of 0.71 g NaPS in43 g DI water was fed separately to the flask for 40 minutes. After theaddition of Stage 1 monomer emulsion the container was rinsed with asmall portion of DI water and added into the flask. The NaPS co-feed wasstopped and the reaction held at 87° C. for 10 minutes. The Stage 2monomer emulsion was fed into the flask over 65 minutes. The NaPSco-feed was re-started and fed for 65 minutes. Furthermore, a separatesolution containing 5.3 g of ammonium hydroxide (28% solution), 20 g ofwater was fed over 65 minutes. After the addition of Stage 2 monomeremulsion the container was rinsed with a small portion of DI water andfed into the flask. The contents of the flask were maintained at 84-86°C. for 5 minutes. The batch was then cooled to 65° C. A redox pair ofhydrogen peroxide aqueous solution and iso-ascorbic acid solution wasfed into the kettle separately. The batch was cooled to roomtemperature.

Polymer PC was prepared substantially as described above, except that:the Stage 1 monomers were added in the amounts of 27.1 g BA, 202.4 gMMA, and 0.5 g MAA; and the Stage 2 monomers were added in the amountsof 64.5 g BA, 392.2 g MMA, and 1.0 g MAA.

Example 2

Preparation of Exemplary Sunscreen Formulations

Exemplary sunscreen compositions E1-E3 according to the presentinvention contain the components recited in Table 2.

TABLE 2 Exemplary Sunscreen Formulations E1 E2 E3 (wt (wt (wt Trade NameINCI %) %) %) Phase A Arcel 986¹ Stearic Acid 0.5 0.5 0.5 DOW CORNINGPEG-10 2 1.4 0.7 ES-5612² Dimethicone Phase B XIAMETER Dimethicone 5 3.61.8 PMX-200 Silicone Fluid² XIAMETER Cyclopentasiloxane 20 14.3 7.1PMX-0245² Titanium Dioxide³ Titanium Dioxide/ 5 5 5 Alumina/JojobaEsters Silica³ Silicone Dioxide 4 4 4 DOW CORNING Silicone Elastomer 10.7 0.4 9045² Phase C Glycerin Glycerin 5 5 5 Dipropylene Dipropylene 33 3 Glycol Glycol 1,3-Butanediol 1,3-Butanediol 2 2 2 EDTAEthylene-diamine- 0.01 0.01 0.01 tetraacetic acid tetrasodium salt DIWater — 35.4 43.4 53.4 Phase D Optiphen⁴ Phenoxyethanol 1 1 1 andCaprylyl Glycol Polymer PE — 16.1 16.1 16.1 (30% solids) ¹Available fromSpectrum Inc. ²Available from Dow Corning/The Dow Chemical Company³Available from Kobo Products, Inc. ⁴Available from InternationalSpecialty Products Inc.

The sunscreen formulations were prepared by mixing all Phase Acomponents into a container and heating to 70° C. Phase B was mixedseparately and heated to 70° C. Phase A and Phase B were combined whilemixing at variable speeds of 800-1,000 rpm for 15-20 minutes. Phase Cwas mixed separately and added into the batch while mixing at variablespeeds of 800-1,000 rpm for 15-20 minutes. Once resulting mixture cooledto 40° C., Phase D was added into the batch while mixing at variablespeeds of 800-1,000 rpm for 10 minutes while further cooling to roomtemperature.

Example 3

Preparation of Comparative Sunscreen Formulations

Comparative sunscreen compositions C1-C4 contain the components recitedin Table 3.

TABLE 3 Comparative Sunscreen Formulations C1 C2 C3 C4 (wt (wt (wt (wtTrade Name INCI %) %) %) %) Phase A Arcel 986¹ Arcel 986¹ 0.5 0.5 0.50.5 DOW CORNING DOW CORNING 2 2 1.4 0.7 ES-5612² ES-5612² Phase BXIAMETER Dimethicone 5 5 3.6 1.8 PMX-200 Silicone Fluid² XIAMETERCyclopentasiloxane 20 20 14.3 7.1 PMX-0245² Titanium Titanium Dioxide/ 55 5 5 Dioxide³ Alumina/Jojoba Esters Silica³ Silicone Dioxide 4 4 4 4DOW CORNING Silicone Elastomer 1 1 0.7 0.7 9045² Phase C Glycerin — 5 55 5 Dipropylene — 3 3 3 3 Glycol 1,3-Butanediol — 2 2 2 2 EDTAEthylene-diamine- 0.01 0.01 0.01 0.01 tetraacetic acid tetrasodium saltDI Water — 51.5 — 59.5 69.5 Phase D Optiphen⁴ Phenoxyethanol 1 1 1 1 andCaprylyl Glycol Polymer CE — — 16.1 — — (30% solids) ¹Available fromSpectrum Inc. ²Available from Dow Corning/The Dow Chemical Company³Available from Kobo Products, Inc. ⁴Available from InternationalSpecialty Products Inc.

The sunscreen formulations were prepared by mixing all Phase Acomponents into a container and heating to 70° C. Phase B was mixedseparately and heated to 70° C. Phase A and Phase B were combined whilemixing at variable speeds of 800-1,000 rpm for 15-20 minutes. Phase Cwas mixed separately and added into the batch while mixing at variablespeeds of 800-1,000 rpm for 15-20 minutes. Once resulting mixture cooledto 40° C., Phase D was added into the batch while mixing at variablespeeds of 800-1,000 rpm for 10 minutes while further cooling to roomtemperature.

Example 4

SPF Boost Study of Sunscreen Formulations Prepared with HydrophilicDispersion

The SPF value of formulations E1 and C1 as prepared in Examples 2 and 3,respectively, were measured using an in vitro technique substantiallyaccording to the following protocol in compliance with the COLIPA 2007method:

Initially, the weight of a roughened PMMA substrate (purchased fromSCHÖNBERG GmbH & Co. KG, Hamburg/Germany,) is measured. The batch to betested is then deposited on the substrate and then quickly leveled witha 7 micron draw down bar to achieve a thin, uniform layer. The layer isallowed to dry for about 20 minutes, and the weight of the substrateplus dry uniform layer is determined. The UV absorption of dry uniformlayer is measured using a LABSPHERE UV-2000S spectrometer at multiplepoints on the layer.

The percent solids of the layer is measured using an OHAUS MB45 solidsanalyzer. Using the weight of the dry film, and the solids content ofthe layer, the weight, and consequently the density of the original wetlayer immediately after deposition can be calculated. Using thisinformation, the SPF can be calculated by the following equation:

${SPF} = \frac{\int_{290\mspace{14mu}{nm}}^{400\mspace{14mu}{nm}}{{E(\lambda)}{S(\lambda)}{\partial\lambda}}}{\int_{290\mspace{14mu}{nm}}^{400\mspace{14mu}{nm}}{{E(\lambda)}{S(\lambda)}10^{({- {A{(\lambda)}}})}{\partial\lambda}}}$Where E(λ)=spectral irradiance of the Standard Sun Spectrum;S(λ)=erythemal action spectrum at wavelength λ; and A(λ)=correctedspectral absorbance at wavelength λ (a correction factor is calculatedto extrapolate the data to establish what the absorbance would be at awet layer density of 2.0 mg/cm² (using the original wet layerimmediately after deposition).

The results of the SPF measurements are shown in Table 4 as percent SPFimprovement from a composition with no copolymer particles having an SPFof 15.51.

TABLE 4 SPF Performance Sunscreen Formulations Formulation SPF SPF Boost(%) C1 7.28 — E1 18.03 147

The results demonstrate that exemplary sunscreen formulations preparedin accordance with the present invention provide a SPF boost valuesignificantly higher than comparative formulations.

Example 5

Dispersion Study of Exemplary and Comparative Sunscreen Formulations

The compatibility study of inventive formulation E1 as prepared inExample 2 and comparative formulations C1 and C2 as prepared in Example3 were evaluated by scanning electron microscopy (SEM) using a FEI NovaNanoSEM 630. The images in FIG. 1 indicate that an improved dispersionresults by inclusion of copolymer particles in accordance with thepresent invention (E1), as compared with formulations in which nocopolymer particles are present (C1) or comparative copolymer particlesare included (C2).

Example 6

Particles Size Distribution of Exemplary and Comparative SunscreenFormulations

The particle size distribution of exemplary sunscreen formulations E1and E2 as prepared in Example 2 and comparative sunscreen formulationsC1, C2, and C3 as prepared in Example 3 were evaluated using asymmetricflow field flow fractionation with multi-angle light scatteringdetection (“A4F-MALS”), which was used to separate the particles in theformulations based on their particle size. The mobile phase of A4F was0.1 weight % FL-70 solution (available from Fischer Scientific) inwater. A RC 10 kDa membrane (available from Wyatt Technology) was usedfor A4f evaluations. The cross-flow profile was turned to be able toseparate a set of polystyrene latex particles between 50 nm and 400 nmdiameter. Because of the need-shape of the TiO₂ used in this study, tobetter illustrate the particle size distribution, the A4F results (lightscattering response at 90° scattering angle vs. elution time) wereplotted against a set of polystyrene particle size standards. Two samplepreparation methods were used to disperse the TiO₂ particles fromsunscreen samples into a buffer solution before A4F analysis.

Sonication Method

The following sonication method was used to disperse the TiO₂ particlesfrom sunscreen formulation samples into a buffer solution before A4Fanalysis. The formulations were diluted 2000 times into a 0.2 wt % FL-70solution in water, followed by a 30 minutes sonication process. Thesonicated solutions were then filtered with 1 μm glass fiber filtersprior to the A4F analysis.

FIG. 2 shows that exemplary formulation E1 demonstrates a much largerlight scattering peak area than the comparative formulations C1 and C2,indicating that formulation E1 has more small particles (i.e., PS<400nm) as compared with formulations C1 and C2. This higher concentrationof small particles is indicative of higher compatibility between thevarious components in the formulation.

Mechanical Shaking Method

The following mechanical shaking method was used to disperse the TiO₂particles in solution. Exemplary sunscreen formulations E1 and E2 andcomparative sunscreen formulations C1 and C3 were diluted 1000 times ina mixture of ethanol and 1 wt % FL-70 solution in water (5:95 w/w). Thediluted samples were shaken on a mechanical shaker for 1 day to dispersethe TiO₂ particles in the solution. The diluted solutions were filteredwith 1 μm glass fiber filters prior to the A4F analysis.

FIG. 3 shows that exemplary formulation E1 demonstrates a much largerlight scattering peak area than comparative formulation C1, indicatingthat formulation E1 has more small particles (i.e., PS<400 nm) ascompared with formulation C1. This higher concentration of smallparticles is indicative of higher compatibility between the variouscomponents in the formulation.

FIG. 4 shows that exemplary formulation E2 demonstrates a much largerlight scattering peak area than comparative formulation C3, indicatingthat formulation E2 has more small particles (i.e., PS<400 nm) ascompared with formulation C3. This higher concentration of smallparticles is indicative of higher compatibility between the variouscomponents in the formulation.

What is claimed is:
 1. A method of protecting skin from UVA and UVBdamage comprising topically administering to the skin a sunscreencomposition comprising: (a) 0.1 to 20 weight % transparent inorganicmetal oxide particles, based on the weight of the composition, whereinthe transparent inorganic metal oxide particles include at least one oftitanium dioxide and zinc oxide; (b) 0.1 to 15 weight % copolymerparticles dispersed in an aqueous medium, based on the weight of thecomposition, wherein the copolymer particles comprise polymerized unitsderived from (i) 0.1 to 20 weight % of phosphorus acid monomers, whereinthe phosphorus acid monomers comprise phosphoethyl methacrylate, and(ii) 80 to 99.9 weight % of comonomers, wherein the comonomers includeat least one of butyl acrylate, methyl methacrylate, methacrylic acid;and (c) 0.1 to 35 weight % silicone fluid, based on the total weight ofthe composition, wherein the silicone fluid includes at least one ofhexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,octamethyltrisiloxane, decamethyltetrasiloxane,dodecamethylpentasiloxane, tetradecamethylhexasiloxane,hexadeamethylheptasiloxane,heptamethyl-3-{(trimethylsily)oxy)}trisiloxane,hexamethyl-3,3,bis{(trimethylsilyl)oxy}trisiloxanepentamethyl{(trimethylsilyl)oxy}cyclotrisiloxane, polydimethylsiloxane,polyethylsiloxane, polymethylethylsiloxane, polymethylphenylsiloxane andpolydiphenylsiloxane; and (d) a dermatologically acceptable carrier. 2.The method of claim 1, wherein the silicone fluid includes a mixture ofdecamethylcyclopentasiloxane and polydimethylsiloxane.
 3. The method ofclaim 1, wherein the sunscreen composition administered to the skincontains 0.1 to 25 wt % of the silicone fluid.
 4. The method of claim 1,wherein the transparent inorganic metal oxide particles are titaniumdioxide.
 5. The method of claim 2, wherein the sunscreen compositionadministered to the skin contains 0.1 to 25 wt % of the silicone fluid.6. The method of claim 2, wherein the transparent inorganic metal oxideparticles are titanium dioxide.
 7. The method of claim 5, wherein thetransparent inorganic metal oxide particles are titanium dioxide.